Look at the code

<form id="payForm" action="yeepaypay.html" target="_blank" method="post" onsubmit="return checkform();">

The onsubmit function in the example is the function that fires before the form is submitted

function checkform() {
var value = $("input[name='payWay']:checked").val();
if (value == 1) {
$("#alipayment").submit();
return false;
}
return true;
}

The form will only be submitted if it returns true, otherwise it will not be submitted